The present invention concerns in general a process for replacing an initial outermost coating layer of a coated optical lens, in particular an ophthalmic lens, with or depositing thereon a layer of a new final coating having surface properties different of those of the initial outermost coating layer.
It has become more and more common in the manufacture of ophthalmic lenses to coat the lenses with one or several functional coating layers for imparting to the resulting ophthalmic lenses various properties such as impact resistance, scratch-resistance, anti-reflective and anti-soiling properties.
Thus, a typical ophthalmic lens may comprise a substrate made of an optically transparent material, such as mineral glass or organic glass, having at least one of its main surfaces coated, successively, with a primer coating layer, a scratch-resistant coating layer, an anti-reflective coating layer, and anti-soiling coating layer (hydrophobic and/or oleophobic top coat).
Typically, the outermost coating layer of an ophthalmic lens is the anti-soiling coating layer (or top coat).
In view of the fast development in the top coat technology, it would be of interest to be able to safely replace an initially deposited hydrophobic top coat by a new top coat having different or improved properties.
Of course, such a replacement of the outermost coating layer by an other one must be effective without adversely affecting the underneath coating layers and/or the substrate, in particular their optical properties.
In particular, the top coat is usually deposited onto an anti-reflective coating layer and the replacement process should not impair the properties of this anti-reflective coating layer.
Also, an ophthalmic lens results of a succession of molding and/or surfacing/polishing operations which determine the geometry of both convex and concave optical surfaces of the lens, and thereafter of appropriate surface treatment as indicated above. The last finition touch of an ophthalmic lens is the edging step which consists in machining the rim or periphery of the lens to conform it to required dimensions for adaptation of the lens into the spectacle mount in which it is intended to be placed.
Edging is generally done on a machine comprising diamond wheels which perform the above defined machining.
The lens is maintained, during this operation, by axial blocking means.
The relative movement of the lens with regard to the wheel is generally numerically controlled in order to obtained the desired shape.
It is thus absolutely necessary that the lens be firmly maintained during the movement.
To this end, before the edging operation a maintaining means is positioned onto the convex surface of the lens.
A maintaining pad, such as an adhesive wafer, for example a double face adhesive, is placed between the maintaining means and the convex surface of the lens.
The thus equipped lens is then positioned on one of the above mentioned axial blocking means, and the other axial blocking means exerts a pressure on the concave face of the lens, through an elastomeric stop.
During machining, a tangent torque is applied onto the lens which may induce a rotation of the lens relatively to the maintaining means if the lens is not sufficiently strongly maintained.
A good blocking of the lens principally depends upon a good adhesion at the interface between the maintaining pad and the convex surface of the lens.
As already mentioned, the outermost coating layer of an ophthalmic lens usually comprises a hydrophobic and/or oleophobic anti-soiling top coat generally formed onto an anti-reflective coating.
One problem associated with such top coats, is that, due to their surface properties, they do no permit to obtain a good adhesion of the interface between the maintaining pad and the convex surface of the lens, this lack of adhesion increasing with the increase of efficiency of the hydrophobic and/or oleophobic top coat.
Therefore, it will be of interest to produce ophthalmic lens with an outermost coating which results in a good adhesion with the maintaining pad for the edging operation and thereafter be able to replace this initial outermost coating by a more efficient or appropriate final coating layer depending on the intended final use.
The document WO 01/68384 discloses an apparatus and method for producing a high energy marking on a surface of an ophthalmic lens, such as a corona discharge, to increase the surface energy of the exposed area and obtain a resulting marking visible by fogging. Only a very small area of the lens surface is exposed and partial removal of the subjacent coating or substrate may be tolerated as it does not affect the optical properties of the lens.
Japanese unexamined patent application laid open 2000-308846 discloses forming an anti-fouling layer having excellent anti-fouling, scratch-resistance and solvent resistance by subjecting the surface of a base material, such as an optical part to a pre-treatment. Pre-treatment can be high frequency plasma, electron beam, ion beam, vapor deposition, sputtering, alkali, acid, corona discharge or atmospheric pressure glow discharge method.
The treated surface can be the outer surface of an anti-reflecting layer. It is further precised that the surface energy of anti-reflecting film is as high as 60 J/m2. Therefore, due to the very high surface energy, the surface treated is the surface of a mineral layer, typically a SiO2 layer of an anti-reflecting stack.